1. Field of the Invention
This invention relates to a process and apparatus for regenerating spent catalyst utilized in hydrocarbon conversion processes. The invention is applicable to fluidized systems wherein finely divided catalyst is continuously recycled between a reaction zone and a separate regeneration or reactivation zone. It is particularly applicable to the regeneration of spent fluid catalytic cracking catalyst.
2. Description of the Prior Art
Catalytic hydrocarbon conversion processes wherein a catalyst that has become partially inactivated due to carbonaceous deposits is regenerated by combustion with an oxidizing gas and in which the regeneration catalyst is recycled to the reaction zone are well known to those skilled in the art.
It is also known that spent catalyst can be regenerated in more than one stage of regeneration (see, for example, U.S. Pat. No. 3,767,566 and Hydrocarbon Processing, September 1972, page 136).
In such prior art processes, the sensible heat of the flue gas produced by the combustion of the carbonaceous deposit of the catalyst is lost to the process. Furthermore, currently, a large degree of afterburn is practiced in some units to keep the carbon monoxide effluent from the regenerator at an absolute minimum. This afterburn is produced since the unit has a large amount of oxygen leaving the top of the bed and the residual carbon monoxide leaving the bed is burned in the dilute phase zone above the bed where little catalyst is present. Since there is no catalyst heat sump, the temperature rises as much as 140.degree. to the 1400.degree.F. .+-. level. Since it is desirable to minimize temperature from the standpoint of minimizing thermal deactivation of the catalyst, any means to reduce this temperature will result in more active catalyst and improved yields of gasoline or improved conversion. The present invention will lower the temperature in the upper part of the regenerator and thereby reduce the degree of afterburn.
Additionally, it is now necessary to quench the regenerator off-gases to about 1200.degree.F. due to temperature limitations on the blading of flue gas expanders or to prevent using very costly alloy materials in the flue gas circuit. The quench is usually a water spray. This spray results in a direct loss of energy from the process due to the unrecoverable heat of vaporization. The present invention will eliminate the need for this spray.
It has now been found that improved results can be obtained in a catalyst regeneration process carried out in a specified manner.